Such transmissions for a motor vehicle are configured inter alia as so-termed dual-clutch transmissions, in which the input shafts of the two partial transmissions can be connected by an associated powershift element to a drive input such as an internal combustion engine or an electric motor, wherein the two powershift elements are then combined by means of a dual clutch. The gear steps that can be obtained with such a transmission are distributed in alternation between the two partial transmissions, so that for example one partial transmission produces the odd-numbered gears and the corresponding other partial transmission produces the even-numbered gears. It is also known to obtain the individual gears by means of one or more gear steps or planes each of which have different transmission ratios. By means of corresponding shifting elements these can be connected into the force flow between the drive input and the drive output, so that a corresponding desired transmission ratio between the drive input and the drive output is obtained in each case.
By alternately allocating the gears between the two partial transmissions it is possible, when driving in a gear associated with one of the partial transmissions, to preselect a subsequent gear in the respective other partial transmission by appropriate actuation of the shifting devices, so that an eventual change to the subsequent gear is enabled by opening the powershift element of the one partial transmission and shortly thereafter closing the powershift element of the other partial transmission. In this way the gears or gear steps of the transmission can be powershifted, which improves the acceleration ability of the motor vehicle since the gearshift takes place essentially without traction force interruption and also makes the shifting process more comfortable for the driver.
Such dual-clutch transmissions can also be made with a drive input and drive output intermediate gear system arranged additionally, so that in the axial direction a more compact structure is produced.
From DE 10 2006 054 281 A1 a transmission of that type for a motor vehicle, in the form of a dual-clutch transmission, is known. In this case the dual-clutch transmission comprises two partial transmissions, each with an input shaft. By connecting the respective input shaft by means of an associated powershift element, the two partial transmissions can in each case be connected in alternation into a force or torque flow from a drive input to a drive output, the input shaft of the first partial transmission being designed as a central shaft of the transmission whereas the input shaft of the second partial transmission is designed as a hollow transmission shaft. Furthermore a drive output shaft is provided, which is designed as the drive output of the two partial transmissions, so that rotation of the drive input can be transmitted by way of a plurality of transmission ratio stages to the drive output, in which transmission the force and torque flow passes via an intermediate gear system. In this case at least two wheel planes are engaged in the force and torque flow by actuating associated shifting elements, and by combining shifting element actuation and the force and torque flow a plurality of gear steps can be obtained by way of corresponding wheel planes. Likewise, non-geared transmission of the rotational movement of the drive input to an output shaft of the drive output can be obtained by actuating appropriate shifting elements.
Further, DE 10 2005 033 027 A1 shows a powershifting dual-clutch transmission for commercial vehicles.
In addition, DE 10 2012 217 503 describes a dual-clutch transmission with twelve gears, including an overdrive gear, the transmission being fully powershiftable. In this case only the highest gear, i.e. the eleventh gear, is used as the overdrive gear. The fifth gear, which is a direct gear, and the sixth gear are in the same partial transmission and shifting from gear five to gear six is carried out as a supported gearshift with the seventh gear as the supporting gear.
Moreover, the applicant knows of a dual-clutch transmission with a range group of planetary design. In this case, two partial transmissions are each connected to a respective input shaft and the output side of each partial transmission is connected to the input shaft of the range group. The second partial transmission comprises two gears with the first two gear planes and the first two shifting elements, whereas the first partial transmission has three gears with the third and fourth gear planes and the direct gear and shifting elements Nos. 3 to 5. The fifth and sixth gear planes serve in this case as drive output constants for forward and reverse with the shifting elements Nos. 6 and 7. The direct gear is the fifth gear in the main transmission. In the sixth gear and the twelfth gear (overdrive gear) the two partial transmissions are coupled. In the coupling gear one of the drive input gear planes Nos. 3 or 4 of the first partial transmission is used as the drive output gear plane for the second partial transmission. The drive output leads on via the shifting element for the direct gear, i.e. the fifth shifting element; thus, the first partial transmission is ‘forced’ in the direct gear. A next-higher gear cannot therefore be powershifted. Furthermore, when changing from the sixth to the seventh gear the traction-force-interrupted range group is shifted and accordingly a shift from the sixth to the seventh gear can only take place with traction force interruption.
This has the disadvantage that the structural complexity of the transmission is relatively great for the number of power-shiftable gears that can be obtained.